Method and apparatus for thermal control of a multiple chamber test system

ABSTRACT

A multiple chamber test system is provided. The multiple chamber test system includes a plurality of test chambers that each include a vibration table. In addition, each of the test chambers is provided with thermally controlled air from a common source. An output plenum for providing thermally controlled air to the test chambers may include a flow control device, to provide the same or similar thermal conditions in each of the test chambers. Where pneumatic actuators are used to impart movement to the vibration tables, the exhaust air from the actuators can be prevented from mixing with the thermally controlled chamber air.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______filed ______, entitled “TEST SYSTEM WITH VIBRATION TABLE”, andidentified as Attorney Docket No. 5866-19-2, the entire disclosure ofwhich is hereby incorporated herein by reference.

FIELD

This invention relates generally to air circulation systems and methodsfor thermal control of a multiple chamber test system.

BACKGROUND

Systems for performing highly accelerated life testing (HALT), highlyaccelerated stress screening (HASS), and highly accelerated stressaudits (HASA) are available to test the reliability and durability ofmanufactured products. More particularly, the durability of products canbe tested using HALT systems and procedures. Products can also be testedfor defects before they are distributed to consumers using HASSprocedures, where all of the products are tested, or HASA procedures, inwhich samples taken from a production run are tested. In general, suchtesting includes subjecting devices under test to vibration energyand/or temperature cycling. Such stresses may be introduced to a deviceunder test by mounting the device under test to a shaker or vibrationtable that is located inside an environmentally controlled test chamber.

Particularly in connection with HASS and HASA programs, including HASSand HASA programs that utilize multiaxis random vibration combined withrapid (greater than 40 C per minute) changes, it is desirable to providesystems that are capable of efficiently testing a large number ofdevices. To this end, test chambers are available that allow vibrationtables to be accessed from multiple sides, facilitating the placement ofdevices under test in the test chamber, and the interconnection of thedevices under test to the vibration table. However, particularly withvibration tables having a relatively large area, there is often at leasta portion of the vibration table surface that is difficult to access,and that is therefore rarely if ever used to support a device undertest. Accordingly, the maximum available throughput of the test chamberis not utilized. The result is that the cost per unit tested is higherthan it would otherwise be. In addition, where a relatively largevibration table surface is provided and/or where at least a portion ofthe vibration table surface is unutilized or underutilized, the volumeof the test chamber is larger than would otherwise be required. Thisresults in a system that uses more energy to effect thermal cycling ofthe chamber than might otherwise be required. A single table with arelatively large area can also be inconvenient, particularly where anumber of devices under test are to be connected to the table.

SUMMARY

Embodiments of the present invention are directed to solving these andother problems and disadvantages of the prior art. In accordance withembodiments of the present invention, a multiple chamber or compartmenttest system is provided. More particularly, multiple test chambers orvolumes, each associated with a vibration table, are provided within asingle cabinet or enclosure, for testing multiple devices or products,referred to herein as devices under test, simultaneously. Each testchamber within the enclosure is provided with temperature controlled airfrom a plenum. In addition, for embodiments in which air poweredactuators or hammers are employed, a table air enclosure can be includedto prevent the actuator exhaust air from mixing with the temperaturecontrolled chamber air.

In order to provide the same or similar thermal conditions in each ofthe multiple chambers, various features have been developed andincorporated into the plenum design. For example, in an intake plenumportion of the air handling system, heating and/or cooling elements aredisposed. Air is drawn through the intake plenum, across the heatingand/or cooling elements, by one or more fans. In accordance withembodiments of the present invention, the fan is of a tangential blowertype design. Moreover, the fan can have a width that is equal or aboutequal to the width of the plenum assembly or a portion of the plenumassembly. The air output by the fan is passed to an outlet portion ofthe plenum assembly. Where the plenum assembly provides air to multipletest chambers that are stacked vertically, the outlet portion of theplenum can be tapered, such that the area of the plenum decreases withincreasing distance from the fan. In accordance with still otherembodiments of the present invention, one or more flow control devicescan be included. More particularly, a flow control device or element canbe disposed within or in communication with the outlet portion of theplenum, to facilitate a balanced distribution of air to the multipletest chambers. Moreover, a flow control device can comprise a diverter,a damper, a valve, or other structure or device for controlling a rateof air flow. In accordance with other embodiments, the effect of a flowcontrol device can be varied. In accordance with still otherembodiments, where pneumatic actuators are employed to operate thevibration tables, enclosures can be provided to keep the exhaust fromthe pneumatic actuators separate from the temperature controlled chamberair that occupies the test area of the chambers.

Methods in accordance with embodiments of the present invention includedistributing air to the chambers of a multiple chamber system equally.This can include controlling the air distributed to the differentchambers such that the rate of air blown into each chamber is equal orsubstantially equal. In accordance with still other embodiments, theestablishment or maintenance of thermal uniformity can include providingdifferent chambers with air from a plenum at different rates. Inaccordance with further embodiments, the method can include varying therate at which air is supplied to one or more of the test chambers. Inaddition, air from sources other than a thermally controlled plenum canbe segregated, to prevent that air from influencing the thermalconditions within the test area of the multiple chambers.

Additional features and advantages of embodiments of the presentinvention will become more readily apparent from the followingdiscussion, particularly when taken together with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of a multiple chamber test system inaccordance with embodiments of the present invention;

FIG. 2 is a front perspective view of a multiple chamber test system inaccordance with embodiments of the present invention, with the frontdoors open;

FIG. 3 is a cross-section side elevation view of portions of a multiplechamber test system depicting some of the features of an air circulationsystem in accordance with embodiments of the present invention;

FIG. 4A is a front elevation view of portions of a multiple chamber testsystem depicting some of the features of an air circulation system inaccordance with embodiments of the present invention;

FIG. 4B is a front elevation view of portions of a multiple chamber testsystem depicting some of the features of an air circulation system inaccordance with other embodiments of the present invention;

FIG. 5A is a bottom perspective view of portions of a vibration tableassembly in accordance with embodiments of the present invention;

FIG. 5B is a bottom plan view of portions of a vibration table assemblyin accordance with embodiments of the present invention;

FIG. 5C is a top plan view of portions of a vibration table assembly inaccordance with embodiments of the present invention;

FIG. 5D is a front elevation view of portions of a vibration tableassembly in accordance with embodiments of the present invention,including vibration table support elements;

FIG. 5E is a side elevation view of portions of a vibration tableassembly in accordance with embodiments of the present invention,including vibration table support elements;

FIG. 6 is a block diagram depicting components of a multiple chambertest system in accordance with embodiments of the present invention; and

FIG. 7 is a flowchart depicting aspects of the operation of a multiplechamber test system in accordance with embodiments of the presentinvention.

DETAILED DESCRIPTION

FIG. 1 is a front perspective view of a multiple chamber test system 100in accordance with embodiments of the present invention. In general, themultiple chamber test system 100 includes a cabinet or enclosure 104that contains multiple individual test chambers 108. In the exampleshown, six test chambers 108 are included in the system 100. However,embodiments of the present invention are not limited to any particularnumber of test chambers 108. In accordance with embodiments of thepresent invention, each individual test chamber 108 includes a vibrationtable, and a thermally controlled environment suitable for performingreliability, durability, and/or defect testing of products.

FIG. 2 illustrates the multiple chamber test system 100 of FIG. 1, withthe access doors 204 opened, to provide access to each of the testchambers 108. With the doors 204 open, some of the components of thetest chambers 108 can be seen. In particular, each test chamber 108includes a shaker or vibration table assembly 208. Each vibration tableassembly 208 generally includes a table 212 having a mounting side orsurface 214 that includes mounting points 216 to which devices undertest can be connected, either directly or through a fixture. Inaddition, each vibration table assembly 208 can be associated with askirt 220 that, together with a vibration table shroud 224, and the sidewalls 228 and center walls 230 defining the lateral extent of the testchambers 108, enclose the actuators and supports (not shown in FIG. 2)associated with the vibration table assembly 208. This allows theclimate controlled air in the test chamber 108 volume to be maintainedseparately from the actuators. For example, the vibration table assembly208 actuators can thus be contained in an environment that is separatedfrom the chamber air provided to the test chambers 108 in which devicesunder test are placed and are subjected to thermal cycling and/orthermal control. As a further example, for systems 100 in whichpneumatic actuators are used, by enclosing the actuators associated witheach table assembly 208 exhaust air from the pneumatic actuatorsassociated with the vibration table assemblies 208 can be prevented frommixing with the chamber air provided to the test chambers 108.

FIG. 2 also shows components associated with the air circulation system232 of the multiple chamber test system 100. In general, the aircirculation system 232 includes at least one air intake 236. Moreover,for each test chamber 108 included in a system 100, the volumeassociated with a test chamber 108 is in communication with at least oneintake 236. In the example system 100 shown in FIG. 2, there is one airintake 236 for each column of three test chambers 108. The aircirculation system 232 additionally includes an intake plenum 240. Theintake plenum 240 receives air through the air intake or intakes 236,and can house or otherwise be in communication with an air circulationfan 304 (see FIG. 3).

FIG. 3 is a cross-section of a system 100 in accordance with embodimentsof the present invention, and in particular shows features of the aircirculation system 232. In general, temperature controlled chamber airis circulated through the multiple test chambers 108 by the aircirculation system 232. In operation, air is drawn into the intakeplenum 240, through an air intake 236, by the air circulation system fan304. The fan 304 may comprise a tangential blower. In addition, multiplefans 304 may be provided. In accordance With embodiments of the presentinvention, the intake plenum 240 houses thermal control elements 306.These thermal control elements 306 can include a heating device 308and/or a cooling device 312. As an example, the heating device 308 cancomprise electrically powered resistance heaters. The cooling device 312can comprise, for example, a liquid nitrogen cooling system.Accordingly, air drawn into the intake plenum 240 can be heated orcooled as needed to provide supply air at a desired temperature to thetest chambers 108 of the system 100. As can be appreciated by one ofskill in the art, the operation of certain types of thermal controlelements 306 can cause increases or decreases in the volume of thechamber air in the air circulation system 232. Therefore, the aircirculation system 232 can include provisions for admitting or releasingair as required to maintain a constant or nearly constant air pressurewith the cabinet 104.

The air drawn through the intake plenum 240 by the fan 304 is passedthrough a fan outlet 316 to an air distribution or outlet plenum 320. Ascan be seen in the figure, the outlet plenum 320 in the illustratedexample has a depth d that generally decreases with distance from thefan outlet 316. In addition, an air outlet 324 is provided for each testchamber 108. The decrease in the depth d of the outlet plenum 320assists in the provision of equal amounts of temperature controlled airto the test chambers 108. In addition, the outlet plenum 320 can includeother features to assist in equalizing the amount of air provided toeach test chamber 108. For example, one or more diverters 328 can beprovided to control the flow of air in the outlet plenum 320.

The air circulation system 232 can include one or more flow controldevices 330. For example, a flow control device 330 comprising one ormore diverters 328 can be included. A diverter 328 can include a surfaceor volume that forms a constriction in the outlet plenum 320. Moreover,a diverter 328 can be located downstream of an air outlet 324. Adiverter 328 comprising a constriction creates an area of elevatedpressure that promotes a flow of air through the air outlet 324immediately upstream of the diverter 328. Accordingly, a diverter 328can be used to balance the flow of air to the test chambers 108. Inaccordance with still other embodiments, a diverter 328 can comprise aconstriction with a movable surface or surfaces 334, to allow the sizeof the constriction in the outlet plenum 320 to be varied, to vary theflow of air through a nearby air outlet 324. Alternatively or inaddition, the air outlet 324 may comprise a flow control device 330 inthe foam of a valve or grille that can be adjusted to control the flowof air through the air outlet 324.

In accordance with other embodiments of the present invention, theoutlet plenum 320 can have a depth that remains constant along thelength of the outlet plenum 320. In accordance with such embodiments,the flow of air from the outlet plenum 320 into individual test chambers108 can be controlled by diverters, dampers, valves, or other flowcontrol devices 330 placed between the fan or fans 304 and one or moreof the test chambers 108. For example, a flow control device 330associated with an outlet 324 that is closest to the fan 304 may berelatively more restrictive than a flow control device 330 associatedwith an outlet 324 that is downstream from the first outlet. Forinstance, an area of an outlet 324 relatively near to the fan 304 mayhave an area that is less than the area of an outlet 324 relatively farfrom the fan 304. By thus differentially configuring the flow controldevices 330, flow to individual chambers 108 can be equalized, eventhough the outlets 324 supplying those test chambers 108 are atdifferent locations relative to the fan 304. In accordance with stillother embodiments, flow control devices 330 can comprise variable flowcontrol devices 330. Moreover, the variable flow control devices 330 maybe under active control. For example, an active flow control device 330may comprise an active diverter 328, with a surface 334 that is movablerelative to a nearby outlet 324. In particular, by moving the surface,the area of the outlet plenum 232 can be increased or decreased. This inturn allows flow through one or more outlets 324 to be adjusted. Asstill other examples, a flow control device 330 can comprise a variabledamper.

FIG. 4A is a front elevation view of portions of an air circulationsystem 232 for a multiple chamber test system 100 in accordance withother embodiments of the present invention. In this exemplaryembodiment, an air intake 236 is provided for each column of testchambers 108, and an air outlet 324 is provided for each of the testchambers 108. In addition, the air circulation system 232 includes first320 a and second 320 b outlet plenums. More particularly, the firstoutlet plenum 320 a is associated with a first column of test chambers108, while the second outlet plenum 320 b is associated with a secondcolumn of test chambers 108. The test system 100 can include two fans304 a and 304 b and each fan 304 can supply air to one of the outletplenums 320 a and 320 b. The two fans 304 can draw air from a commonintake plenum 240. Accordingly, each outlet plenum 320 a and 320 b maybe associated with a fan 304. For example, the illustrated embodimentmay incorporate two tangential fans 304, with one fan 304 a supplyingair to the first column of test chambers 108 via the first outlet plenum320 a, and the second fan 304 b supplying air to the second column oftest chambers 108 via the second outlet plenum 320 b. In addition, eachoutlet plenum 320 a and 320 b includes one or more flow control devices330. For example, the area of the outlets 324 can vary with distancefrom the inlet plenum 240. Moreover, one or more of the flow controldevices 330 can comprise variable devices. For example, the diverters328 and/or outlets 324 can be operated to selectively vary the flow ofair past or through the flow control devices 330. Where variable flowcontrol devices 330 are provided, they may be under active control. Thewidth and/or depth of the outlet plenums 320 can decrease withincreasing distance from the fan 304 supplying climate controlled air tothe outlet plenum 320. Alternatively, for example where diverters 328 orother flow control devices 330 are included, the depth and width of theoutlet plenums 320 can remain constant.

FIG. 4B is a front elevation view of portions of an air circulationsystem 232 for a multiple chamber test system 100 in accordanceembodiments of the present invention. In this exemplary embodiment, anair intake 236 is provided for each column of test chambers 108. Inaddition, an air outlet 324 is provided for each of the test chambers108. Accordingly, the air circulation system 232 in this embodimentincludes air intakes 236 and air outlets 324 that are generally disposedin two parallel columns. In this example, the width W of the outletplenum 320 is constant. In accordance with other embodiments, the widthW may decrease as the distance from the fan 304 increases. Accordingly,whether the width W and/or the depth d of the outlet plenum decreases,the volume of the outlet plenum can decrease with increasing distancefrom the fan 304. Although the air intakes 236 and air outlets 324 maybe arranged in parallel columns, the fan 304, the intake plenum 240, andthe thermal control elements 306 within the intake plenum 240 can becommon to the air circulation system 232. Accordingly, these commoncomponents of the air circulation system 232 can supply thermallycontrolled air to the test chambers 108 of the system 100.

As can be appreciated by one of skill in the art after consideration ofthe present disclosure, the arrangement of the air circulation system232 can be varied, in order to accommodate different test chamber 108configurations. The arrangement of intakes 236 and air outlets 324 cantherefore be varied accordingly. In general, the air circulation system232 can include at least one intake 236 for each column of test chambers108, and at least one air outlet 324 for each test chamber 108. Inaddition, it should be appreciated that the air circulation system 232need not comprise a closed loop system.

With reference now to FIGS. 5A-E, different views of a vibration tableassembly 208 that may be included in a test system 100 in accordancewith at least some embodiments of the present invention are illustrated.In general, the table 212 includes a first side or mounting surface 214that may include a plurality of fixture or fastener points 216. Thetable 212 is supported on a second side 504, opposite the mountingsurface 214, by one or more supports or table mount springs 508. Thesprings 508 are mounted in-board of the edges of the table 212. Forexample, the springs are centered on points 512 that form corners of arectangle that is itself centered in the rectangle 514 (see FIG. 5B)defined by the mounting surface 214, and that defines an area that isequal to no more than 50% of the area of the mounting surface 214. Byproviding an in-board mounting location for the springs 508, the table212 can better support a device under test as compared to a vibrationtable in which the springs are mounted at or close to the outerperiphery of the table.

In addition, a plurality of actuators or hammers 520 are interconnectedto the second side 504 of the table 212. The actuators 520 can compriseany type of actuators. For example, pneumatically operated actuators,electric motor actuators, hydraulic actuators, and/or any other type ofdevice capable of accelerating or imparting force to a table 212 can beused. In accordance with embodiments of the present invention, theactuators 520 are configured to provide movement of the table 212 inboth translation and rotation with respect to the x, y and z axes.Accordingly, the vibration table assembly 208 can provide table motionhaving six degrees of freedom. As shown in FIGS. 5D and 5E, a vibrationtable support 524 can provide perches or supports 528 for the springs508 adjacent or facing the second side 504 of the table 212. As can beappreciated by one of skill in the art after consideration of thepresent disclosure, the vibration table support 524 is fixed to thecabinet 104.

As previously mentioned, each vibration table 208 can be associated witha shroud 224. The shroud 224 defines an enclosed volume that containsthe springs 504 that support the table 212 and the actuators 520 thatimpart motion to the table 212. In particular, the enclosed volumemaintains a separation between the chamber air supplied by the aircirculation system 232 and the air surrounding the actuators 520 andsprings 508 of the vibration table. For example, where the actuators 520comprise pneumatic hammers, the exhaust air from the actuators 520 canthus be prevented from mixing with and influencing the temperature ofthe chamber air. As shown in FIG. 2, the shroud 224 can include a frontpanel or portion 226. For a test chamber 108 that is positioned aboveanother test chamber 108, the shroud 224 can also include a bottom panelor portion 332 (see FIG. 3). Moreover, the bottom panel or portion 332can be a separate component, or can comprise a surface of the vibrationtable support 524.

FIG. 6 is a block diagram depicting components of a multiple chambertest system 100 in accordance with embodiments of the present invention.As shown in FIG. 6, the multiple chamber test system 100 includes an aircirculation system 232, a vibration table actuation system 604, and acontrol system 608. In general, the control system 608 receives input612 that is supplied to a controller 616 to control aspects of theoperation of the multiple chamber test system 100. The input 612 caninclude input entered through an input device by a user. The input 612can also include programmed control parameters. The controller 616 maycomprise a general purpose programmable processor, a controller withintegrated memory, or other processor or computer implemented device forexecuting instructions. The instructions that are executed by thecontroller 616 may be in the form of user input, programmed instructionsstored in memory or data storage as software, and/or encoded firmware.More particularly, the controller 616 may execute a control algorithmthat implements or comprises a proportional-integral-derivative (PID)control system. Moreover, a controller 616 in accordance withembodiments of the present invention can include multiple processors,memory devices, and/or logic devices. As generally described herein, thecontrol system 608 can provide control signals to the air circulationsystem 232 and the vibration table system 604. In addition, thecontroller system 608 can receive signals from sensors associated withthe air circulation system 232 and/or the vibration table actuationsystem 604.

Control signals provided by the control system 608 to the aircirculation system 232 include signals provided to the thermal controlelements 306 located in the intake plenum 240. In particular, controlsignals provided by the control system 608 can direct the thermalcontrol elements 306 to heat or cool the air in the intake plenum 240.The control system 608 can also include control signals to controloperation of the fan 304. In addition, the control system 608 canprovide control signals to active flow control devices 330, includingbut not limited to variable outlets 324, variable diverters 328, orvariable dampers 606. As depicted in FIG. 6, air drawn through the airinlet 236 of the air circulation system 232 is received in the intakeplenum 306, where the air can be heated or cooled at the direction ofthe control system 608 by the thermal control elements 306. Moreover,the air is drawn in through the air inlet 236 and the intake plenum 240,across the thermal control elements 306, by the fan 304. The heated orcooled air is then passed by the fan 304 to the outlet plenum 320. Fromthe outlet plenum 320, the air is passed through air outlets 324 toindividual test chambers 108. In the illustrated example, the outletplenum 320 supplies air to a first outlet 324 a associated with a firsttest chamber 108 a, a second outlet 324 b associated with a second testchamber 108 b, and an nth outlet 324 n associated with an nth testchamber 108 n. Accordingly, heated or cooled air is provided to aplurality of test chambers 108. Moreover, an air circulation system 232in accordance with embodiments of the present invention can beconfigured such that heated or cooled air is supplied to any number oftest chambers 108. Air provided to the test chambers 108 is drawn backinto the intake plenum 240 through the air inlet or inlets 236.Accordingly, the air circulation system 232 can recirculate thermallycontrolled test chamber air. Alternatively or in addition, the aircirculation system 232 can admit air from the ambient environment, orrelease air to the ambient environment, to control pressure levelswithin the test chambers 108.

The air circulation system 232 may make use of feedback in connectionwith control signals provided by the control systems 608. In particular,one or more of the test chambers 108 a may include a temperature sensor620. The temperature sensor 620, which as an example can comprise athermocouple, can send a temperature signal to the controller 616. Thecontroller 616 can use the information regarding the temperature of thetest chamber 108 provided by the temperature sensor 620 to control thethermal control elements 306, the fan 304 and/or active flow controldevices 330 such that air of a desired temperature is provided to thetest chambers 108. In the figure, a temperature sensor 620 a, 620 b, and620 n is associated with each of the first 108 a, second 108 b and nth108 n test chambers. Accordingly, the controller 616 can use atemperature signal provided by any one of the temperature sensors 620 tocontrol operation of the air circulation system 232. Alternatively, anaverage temperature sensed by the temperature sensor 620 can be used bythe controller 616. In accordance with still other embodiments of thepresent invention, the controller 616 can operate in response to asignal provided by any one of the temperature sensors 620.Alternatively, a temperature sensor 620 need only be provided in one ofthe test chambers 108, and the signal from that one temperature sensor620 can be used to control the air circulation system 632. In accordancewith still other embodiments, a temperature sensor 620 can be providedin another portion of the air circulation system 232, such as the intakeplenum 240 or in an outlet plenum 320. In accordance with still otherembodiments, for example where variable air outlets 324 and/or diverters328 are included as part of the air circulation system 232, thecontroller 616 can operate to control those variable elements. Moreover,additional sensors can be included to provide signals used by thecontroller 616 in connection with control of the air circulation system232. For example, one or more pressure sensors can be disposed withinthe air circulation systems 632, to provide a signal to the controller616.

The controller 616 can also be operated to control operation of thevibration tables 208. More particularly, in the example illustrated inFIG. 6, the vibration table actuation system 604 comprises apneumatically operated system. Accordingly, a source of supply air 624provides operational air to a set of valves 628. For example, valves 628may be provided for each set of actuators 520 included in the vibrationtable assemblies 208 having a particular orientation. Manifolds 632 thendistribute the air supplied by the valves 628 to those actuators 520. Ascan be appreciated by one of skill in the art, operation of theactuators 520 imparts accelerations on the tables 212. The exhaust airfrom the actuators 520 can be collected in an exhaust plenum 636. Theair from the exhaust plenum 636 may be passed to the ambientenvironment. In accordance with still other embodiments, individualexhaust lines may be used to vent exhaust air directly from theactuators 520 to the ambient environment.

One or more of the tables 212 may have an accelerometer 640 mountedthereto. Accordingly, as shown in the figure, each table 212 may beassociated with an accelerometer 640 a, 640 b and 640 n respectively.Signals from the accelerometer 640 can then be provided to thecontroller 616, and a selected one of the signals, or an average of thesignals, can be used by the controller 616. In accordance with otherembodiments of the present invention, only one of the tables 212 needsto be associated with an accelerometer 640.

A method for providing a test system in accordance with embodiments ofthe present invention is illustrated in FIG. 7. The method may beperformed by or in association with the execution of a control algorithmby the controller 616. According to the method, a plurality of testchambers 108 are disposed within an enclosure 104 (step 704). Each testchamber is associated with a vibration table assembly 208. In addition,the enclosure includes an air circulation system with at least oneintake 236 and at least one air outlet 324 in communication with eachtest chamber 108. The cabinet door or doors 204 are opened to access theplurality of test chambers 108 (step 708). At least one device orproduct under test is then placed on and interconnected to eachvibration table 208 (step 712). After the devices to be tested have eachbeen interconnected to a vibration table 208, the cabinet door or doors204 are closed (step 716).

Operation of the air circulation system can then be initiated (step720). In particular, the fan or fans 304 can be turned on, to draw airin through the air inlet or inlets 236, through the intake plenum 240and across or part the thermal control elements 306. The now heated orcooled air is then forced down the outlet plenum 320 and out the airoutlets 324 into the test chambers 108. In accordance with embodimentsof the present invention, forcing the air out the air outlets 324 caninclude diverting the air in the outlet plenum 320. More particularly, adiverter may be disposed within the outlet plenum, downstream of an airoutlet 324, that forms a constriction to promote a flow of air throughthe air outlet 324. This use of diverters 328 allows pressures at theair outlets 324 to be equalized, to provide identical or near identicalair flow and thermal conditions or stresses to devices under test ineach of the test chambers 108. Alternatively or in addition, air outlets324 and/or dampers 606 or other flow control devices 330 that can beactively controlled can be provided.

Operation of the vibration tables 208 can also be initiated after thecabinet doors 204 are closed (step 724). In accordance with embodimentsof the present invention, the vibration tables 208 may accelerate anattached device, and may do so with six degrees of freedom. Inaccordance with further embodiments of the present invention, all of thevibration tables 208 are operated to impart the same series ofaccelerations to attached devices, such that identical stresses areimparted to the devices. Control of the vibration tables may be inconnection with information provided by an accelerometer. Theaccelerometer may be attached to one of the vibration tables 208.Alternatively, more than one or even all of the vibration tables 208 mayinclude an accelerometer.

At step 728, a determination can be made as to whether the run time forthe test or burn in procedure being performed has been completed. If therun time has been completed, the process may end. Otherwise, the processwill continue until the prescribed run time has been reached (step 732).

Although certain examples have depicted and described a test system 100including an enclosure 104 housing six test chambers 108 disposed in twocolumns of three, embodiments of the present invention are not limitedto such a configuration. In general, embodiments of the disclosedinvention have application to any test system 100 incorporating aplurality of test chambers 108. In addition, although an enclosure 104with front doors 204 only is illustrated, embodiments of the presentinvention can have doors configured to allow access to test chambers 108as deemed necessary or convenient for a particular use or application.In accordance with embodiments that make use of a common controller 616,the controller 616 can operate by executing a single copy or instance ofa control algorithm. Accordingly, multiple test chambers 108 can beprovided with thermally controlled air, and vibration tables 212 in eachof the test chambers 108 can be operated in a like manner using a singlecontroller 616 and control algorithm. In connection with suchembodiments, a temperature sensor 620 associated with any one of thetest chambers 108 or any other portion of the air circulation system 232to provide temperature information to the controller 616. A singleaccelerometer 640 associated with any one of the tables 212 can be usedto provide the controller 616 with acceleration information. Inaccordance with such embodiments, it is advantageous that the testchambers 108, vibration table assemblies 208 and attached devices undertest be configured identically. Although various examples providedherein discuss the use of pneumatic actuators 520, any type of actuatormay be used.

The foregoing discussion of the invention has been presented forpurposes of illustration and description. Further, the description isnot intended to limit the invention to the form disclosed herein.Consequently, variations and modifications commensurate with the aboveteachings, within the skill or knowledge of the relevant art, are withinthe scope of the present invention. The embodiments describedhereinabove are further intended to explain the best mode presentlyknown of practicing the invention and to enable others skilled in theart to utilize the invention in such or in other embodiments and withvarious modifications required by the particular application or use ofthe invention. It is intended that the appended claims be construed toinclude alternative embodiments to the extent permitted by the priorart.

1. A test system, comprising: a test cabinet; a plurality of testchambers, wherein the test chambers are disposed within the testcabinet; an air circulation system, including: an air intake; aplurality of air outlets, wherein at least one air outlet is associatedwith each test chamber in the plurality of test chambers; an intakeplenum; a fan, wherein the fan is supplied with air from the intakeplenum; an outlet plenum, wherein the fan supplies air to the outletplenum; a plurality of vibration tables, wherein each test chamber inthe plurality of test chambers includes at least one vibration table. 2.The system of claim 1, further comprising; a vibration table shroud,wherein at least one of the vibration tables is associated with avibration table shroud.
 3. The system of claim 2, wherein the at leastone of the vibration tables associated with the vibration table shroudis disposed above another vibration table.
 4. The system of claim 2,further comprising: a plurality of vibration table actuators, whereineach vibration table in the plurality of vibration tables is associatedwith a vibration table actuator, and wherein the vibration table shroudof the at least one of the vibration tables encloses the vibration tableactuator for that vibration table and defines a volume that is separatefrom the air circulation system.
 5. The system of claim 2, wherein theat least one vibration table shroud associated with the vibration tabledisposed above another vibration table includes a front panel and abottom panel.
 6. The system of claim 2, wherein all of the vibrationtables are associated with a vibration table shroud, wherein at leastone vibration table shroud associated with a vibration table at a bottomof a column of vibration tables includes a front panel, and wherein atleast one vibration table shroud associated with a vibration tabledisposed above another vibration table includes a front panel and abottom panel.
 7. The system of claim 1, further comprising: at least onediverter, wherein the at least one diverter is disposed inside theoutlet plenum, and wherein the at least one diverter forms a constrictedarea within the outlet plenum.
 8. The system of claim 7, wherein the atleast one diverter is downstream of at least one of the air outlets. 9.The system of claim 8, wherein the at least one diverter is upstream ofanother one of the air outlets.
 10. The system of claim 1, furthercomprising at least a first flow control device.
 11. The system of claim10, wherein the at least a first flow control device comprises one of adiverter, a damper, a valve, and an outlet.
 12. The system of claim 10,wherein the flow control device is an active flow control device. 13.The system of claim 1, wherein the fan is a tangential fan.
 14. Thesystem of claim 1, further comprising: a thermal control element,wherein the thermal control element is disposed within the intakeplenum.
 15. A multiple chamber test system, comprising: a cabinet; atleast one door; a plurality of test chambers, wherein each of the testchambers is disposed within the cabinet; a plurality of vibrationtables, wherein each test chamber includes at least one vibration table,and wherein each of the vibration tables is accessed through the atleast one door; an air circulation system, including at least oneintake, an outlet plenum, at least one diverter disposed within the airoutlet plenum, and a plurality of air outlets, wherein each test chamberin the plurality of test chambers is associated with at least one airoutlet.
 16. The system of claim 15, wherein the plurality of testchambers are arranged to form at least one column of test chambers,wherein a vibration table shroud is associated with each test chamberthat is above any other test chamber.
 17. The system of claim 15,further comprising: at least one vibration table shroud, wherein atleast one test chamber in the plurality of test chambers is associatedwith a vibration table shroud.
 18. A method for providing a test system,comprising: providing a cabinet enclosing a plurality of test chambers;drawing air into an air circulation system through an intake incommunication with at least some of the test chambers; forcing airthrough an air outlet plenum, wherein the air outlet plenum includes aplurality of air outlets in series, and wherein each test chamber in theplurality of test chambers is associated with an air outlet; divertingair from the air outlet plenum through at least one air outlet.
 19. Themethod of claim 18, wherein each test chamber includes a vibrationtable, the method further comprising: interconnecting a device undertest to each vibration table; using the air circulation system,circulating air at a controlled temperature through the plurality oftest chambers; operating the vibration tables, wherein the vibrationtables are moved using pneumatic actuators, and wherein exhaust air fromthe pneumatic actuators is segregated from the air circulated throughthe air circulation system.
 20. The method of claim 19, wherein atemperature within each of the test chambers is about the same at anyone point in time.